Well this seems pretty cool, http://codility.com

Although, it seems to just quiz you about basic asymptotic growth and does not seem to look at things like programming style etc. Still, I'm please my Ruby answer for the demo test got 100%, which, as the histogram shows... Not many people get. I suspect that the reason is, many people probably submit an O(n^2) answer, which fails for very large data sets. Here is what I submitted

And here is what I submitted:

def equi(arr)
  lhs = 0
  tmp = 0
  rhs = arr.inject(0) { |a,b| a + b }
  arr.each_index do |i|
    lhs += tmp
    rhs -= arr[i]
    tmp = arr[i] 
    return i if lhs == rhs
  end
  return -1
end

And Here's the analysis it gave back to me:

test time result
example
Test from the task description 		0.012 s. OK
extreme_empty
Empty array 		0.020 s. OK
extreme_first 0.008 s. OK
extreme_large_numbers
Sequence with extremly large numbers testing arithmetic overflow. 		0.020 s. OK
extreme_last 0.012 s. OK
extreme_single_zero 0.020 s. OK
extreme_sum_0
sequence with sum=0 		0.020 s. OK
simple 0.016 s. OK
single_non_zero 0.012 s. OK
combinations_of_two
multiple runs, all combinations of {-1,0,1}^2 		0.008 s. OK
combinations_of_three
multiple runs, all combinations of {-1,0,1}^3 		0.012 s. OK
small_pyramid 0.072 s. OK
large_long_sequence_of_ones 13.349 s. OK
large_long_sequence_of_minus_ones 10.781 s. OK
medium_pyramid 4.336 s. OK
large_pyramid
Large performance test, O(n^2) solutions should fail. 		21.369 s. OK